Genetic and environmental factors contribute to systemic lupus erythematosus (SLE). Previous studies showed environmental factors such as bacterial products or their-induced inflammatory mediators (e.g., IFN-?) are involved in SLE pathogenesis. Previous studies from others and we revealed that multiple autoAbs are more commonly detected in first-degree relatives of lupus patients (FDRs), compared to unrelated healthy controls (UHCs). In addition, FDRs have heightened levels of inflammation (e.g., B lymphocyte stimulator (BLyS), and IFN-?) associated with TLR stimulation and B cell activation compared with UHCs. It is unclear the initial trigger for autoantibody production. This lack of understanding of early events in development of autoimmunity is a critical barrier for disease prevention. FDRs, rather than patients, provide a study population, genetically prone and possibly environmentally exposed, who are not on immune modulatory drugs nor impacted by disease, allowing conclusions less confounded by external factors. In preliminary studies, we found: 1) increased presence and diversity of autoAbs in healthy FDRs of lupus patients compared to unrelated healthy controls (UHCs); 2) increased microbial product translocation (plasma LPS) associated with elevated plasma autoAb levels (anti-dsDNA, anti-ssDNA, and anti-nucleosome); and 3) decreased plasma microbial diversity in FDRs with enrichment of the family Streptococcaceae and genus of Streptococcus product translocation in UHCs and relative enrichment of Pseudomonas product translocation in FDRs relative to UHCs. Recently SNPs in the coding region of two genes that mediate gut permeability were identified as associated with lupus disease risk. We hypothesize that increased gut microbial product translocation and its-associated inflammation in FDR individuals, a result of a ?leaky? gut, serve as initiators for autoAb production and later SLE development. In the current study, we will recruit matched UHCs, FDRs, and lupus patients. A ?leaky? gut leading to systemic bacterial products and autoAb induction in the pathogenesis of lupus represents a novel mechanism to explain disease initiation in susceptible genetic high- risk individuals. Specific Aim 1: Determine intestinal barrier integrity, systemic bacterial product translocation, and its mediated inflammation in the activation of B cells. We hypothesize that plasma autoAb levels are associated with intestinal barrier integrity, inflammation and systemic bacterial products. In vivo gut permeability tests, plasma LPS and total bacterial rDNA levels, plasma TLR-related inflammation (e.g., IL-6 and IFN-?), B cell subset activation and a series of lupus-related autoAbs (e.g., anti-dsDNA and anti-nucleosome IgGs) will be assessed in patients, FDRs and UHCs. Specific Aim 2: Determine systemic and mucosal microbial components and the effect of certain bacterial product translocation on autoantibody production. We have observed relative enrichment of Pseudomonas products in plasma of FDRs relative to UHCs. Comparisons between systemic and mucosal microbiomes has not been reported previously in lupus patients, FDRs or UHCs. We therefore will assess the systemic and mucosal microbiome and identify the role of microbial translocation in autoAb production and lupus disease in both human and mouse studies. In the current study, we propose to investigate a novel mechanism for autoAb production and SLE etiology. We believe that a broad array of TLR agonists, from a ?leaky? gut, are the fundamental drivers of autoAb initiation. This work will provide insight into the potential of a therapeutic strategy targeting mucosa or particular bacteria to prevent autoAbs and disease onset.